Known in the art are communication systems for friend-or-foe (IFF) identification which typically include laser emitters mounted on aiming devices (e.g. mounted on firearms), which trigger light detectors on potential targets. For example, in a known IFF system described in the European patent No. 254,197, a laser signal and a radio signal are simultaneously transmitted towards a potential target. Upon receiving these two signals by detectors in a responder unit mounted on the target, the responder generates a radio signal response confirming its identity.
However, in general, wave-beams (such as, for example, light wave-beams, radio-frequency wave-beams, or acoustic wave-beams) diverge as they propagate: the wave-beam's lateral extent increases with the distance from the wave-beam's source (e.g. due to diffraction). Typical wave-beams such as electromagnetic and/or acoustic beams (e.g. laser beams) can be conveniently modeled in the para-axial approximation as a Gaussian wave-beam. This serves as a good model for the basic propagation mode of a wave-beam (TM 00). The following considers this basic mode, which, if needed, can be expanded to include higher order modes utilizing Gaussian, Hermite-Gaussian, Laguerre-Gaussian functions and/or combination thereof.
Gaussian beams maintain a nearly constant width with substantially no beam divergence near the beam “waist” (e.g. near the focal region) at which the wavefronts are planar, and normal to the direction of propagation. However, as the distance from the beam waist grows, a Gaussian beam asymptotically approaches a constant divergence (similar to that described by geometric ray optics).
Therefore, standard wave-beams with a Gaussian beam form are typically not used in cases where constant beam width is required along an extended range along the propagation axis of the beam. An extended range of constant beam-width may be achieved with Bessel beams whose amplitude distribution is described by a Bessel function of the first kind. However, although such beams do not diverge, ideal Bessel beams are difficult to generate in practice (as they require an unbounded/infinite illumination source). To this end, in applications requiring substantially constant beam-width along the propagation axis, Pseudo Bessel beams are typically used, formed in practice by focusing a Gaussian beam with an axicon lens. Nevertheless Pseudo Bessel beam approximations are practical only for limited distances/ranges because the constant-width beam gradually diffracts the light away from the region of interest, thereby causing intensity loss (which is not replenished due to the use of finite light source).
General Description
Generation of wave-beams having decreased or no divergence within the desired range of distances from the source of the beams may be advantageous for various applications, for example for applications in which the area illuminated by the wave-beam serves to define a region of interest. For example such applications include friend-or-foe identification (IFF) as well as laser-based bilateral simulation and training systems, and the Multiple Integrated Laser Engagement System (MILES).
Conventional applications such as MILES and IFF, which utilize common diverging laser beams to designate/define a region of interest, may not be effective or accurate enough to simulate the ammunition's hits and/or to identify friendly forces at both short and long ranges. This is due to the laser beam's divergence causing the illumination of a small cross-sectional area at short range and a larger cross-sectional area at larger ranges. The situation is exacerbated when the illuminated area is required to be much larger than the laser beams' source diaphragm/aperture (e.g. the optical aperture of the laser's output port), since to larger divergences are needed to achieve wider illumination cross-section areas. For example, considering a MILES illumination laser device for foot-soldier's weapon, the radius of its laser exit aperture may be in the order of few millimeters (e.g. 5 mm) while it may be required to illuminate/define an area of a region of interest extending several meters (e.g. illuminate a spot diameter of 500 mm at a distance of 300 m) in order to simulate a hit. To this end, utilizing conventional techniques with a Gaussian or near-Gaussian beam, the region of interest is not properly covered as the lateral extent/diameter of the spot varies significantly with the distance from the source of the beam (e.g. in the above example the spot diameter would be approximately only 250 mm at a distance 150 m, which is considerably smaller than the desired 500 mm value).
The use of pseudo Bessel beams, which potentially offer a fixed lateral extent as they propagate, are impractical and can be achieved in practice only over limited distances. This is because generation of a pseudo Bessel beam having practically constant lateral extent over a large range requires a beam source having large lateral dimensions (physical size), as well as very large power requirements of the beam's source (e.g. laser). Additionally, larger lateral dimensions of the beam's source are needed in cases where wider constant lateral extent of the beam is required and/or where the beam should have the constant lateral extent for longer distances.
The present invention provides a technique for generating a wave-beam (such as a light beam, radio-frequency beam, acoustic beam) having a substantially constant lateral extent (cross-sectional width) over a desired range of distances from the beam's source, while overcoming the aforementioned deficiencies of the known techniques. Moreover, according to the invention, provided are systems and methods capable of generating wave-beams whose substantially constant lateral extent is substantially larger than the lateral-extent/radius of the output aperture/diaphragm of the beam's source. This enables use of a small beam generator for producing wave-beams having substantially wider and constant lateral extent over a desired range.
According to this novel technique, a plurality of wave-beams (i.e. also referred to herein as component/constituent wave-beams e.g. light beams, radio frequency beams, or acoustic beams) having different divergences are superposed in at least a partial incoherent manner. This at least partial incoherency creates a combined beam (also referred to herein as interrogation wave-beam) having substantially constant lateral extent over a desired range of distances from the beam's source. In some embodiments, the constituent wave-beams are fully incoherent. This is achieved by producing beams which differ in optical path length by more than the coherence length and/or in wavelength, and/or in polarization, and/or in temporal occurrence (as shall be clarified below). In other embodiments, the constituent wave-beams are partially incoherent (as shall be clarified below).
It should be understood that in the scope of the present disclosure the term constant lateral extent and/or constant radius/diameter of a wave-beam refers to the cross-sectional width over a desired range along the propagation axis of the wave-beam, for which the amplitude or intensity (which is proportional to the amplitude squared) of the combined interrogation wave-beam is larger than or equal to a certain threshold amplitude or intensity. In other words the terms lateral extent/radius/dimensions of the beam relate to the dimensions of a cross-sectional contour of the beam at which the beam's intensity (e.g. or an integral of the intensity over a predetermined period of time, such as a detector's integration time) substantially equals a certain detection threshold value, while within this contour the intensity/integral-intensity is higher than the detection threshold, and outside thereof it is lower than the detection threshold. In practice the constant lateral extent, may be evaluated with devices that have a intensity detection threshold, and as such introduce a tolerance on this detection threshold, due, for example to angular misalignment of a detector with the incident wave-beam. Such a detection tolerance effectively introduces two threshold values (i.e. upper-limit and lower-limit intensity thresholds being respectively higher and lower than the nominal detection threshold). In other words, in the following a wave-beam is considered to have a desired constant lateral extent at a certain operating range, when at the boundary of the desired lateral extent, the beam's intensity is in-between the upper-limit and lower-limit intensity thresholds. In this regards, in some cases the upper-limit and lower-limit intensity thresholds may be respectively higher and lower by about 10% from the nominal detection threshold, and in some cases up to ±30% from the nominal detection threshold, while the beam is still considered to have the constant lateral extent.
In this connection, it should be noted that the term intensity used herein, should also be understood, where appropriate, as relating to an integral of the intensity over a period of time associated with the integration time of a detector designated for sensing/detecting the beam. Accordingly, in forming the interrogation wave-beam the constituent wave-beams may be superposed substantially simultaneously, wherein simultaneously should be understood in the sense that the beams are projected at the same time and/or at slightly different times, such that they co-exist within a timeframe in the order of or shorter than an integration time of a designated detector by which they are to be sensed. In this connection, in cases where the constituent wave-beams are projected at the same time, they should be at least partially incoherent with respect to one another so as to reduce interferences between them. Coherent constituent wave-beams projected at different times would generally not interfere, and in cases where they are projected within a time frame shorter than a detector's integration time, they would be sensed together as simultaneous incoherent beams by the detector. In this sense, such beams are considered in the following as at least partially incoherent beams.
Also, it should be noted that the terms illuminate, illuminating and/or illumination are used herein in their broad sense to designate “illumination” and/or interrogation by any type of wave-beam, which may be for example an acoustic-, optical- and/or radio-frequency wave-beam. Accordingly, these terms should not be construed as relating solely to optical/light beams.
It is understood that in incoherent superposition of two or more wave-beams, interference does not occur at all. In a partially coherent superposition (which is also referred to as “partially incoherent superposition” in this document), interference occurs, but the quality/strength of the interference pattern typically measured by its range of intensities between maximum and minimum (visibility in the non limiting example in which the wave-beams are light beams), is reduced (e.g. no portion of the interference pattern is completely dark). In some embodiments, this partial coherence between beams is sufficient for generating a combined wave-beam having substantially constant lateral extent over a desired range. Partial/full incoherence may be obtained by superposition of wave-beams whose optical path lengths differ to various extents (e.g. greater than a coherence length of the beams), and/or wave-beams of different wavelengths, and/or different polarizations (e.g. a combination of linearly-polarized and circularly-polarized wave-beams may provide partial incoherence), and/or beams having different temporal occurrences (which may be perceived as simultaneous by a designated detection module as clarified above). While small differences in such properties may be insufficient to render two wave-beams completely incoherent, it may be sufficient to ensure their partial incoherence necessary for the applications in this disclosure. Specifically, as long as the minimal fringe intensity is larger than, for example, twice the intensity threshold used to define the lateral extent of the wave-beam (as further clarified below), the partially coherent superposition between wave-beams is suitable for some applications of the disclosed invention.
An advantage of the present invention lies in its implementation of readily available wave-beam forms, such as Gaussian, or near Gaussian beams. Furthermore, contrary to pseudo Bessel beams, which can also offer a limited range of constant beam width, the present invention provides for a wave-beam having a constant lateral extent over extended distances and which can be significantly larger than the aperture of the wave-beam's source. Optionally, the lateral extent of the combined beam and/or the range at which the lateral extent of the beam remains substantially constant is adjustable, by adjusting the divergences and/or intensities of one or more of its constituent wave-beams, and/or by emitting and combining only part of the plurality of the constituent wave-beams.
To this end, according to the present invention there is also provided a novel IFF system and method having improved accuracy and reliability as well as providing for interrogation capability in near line-of-sight. This is achieved according to the invention by utilizing an interrogation system capable of generating an interrogation wave-beam (e.g. optical, radio frequency and/or acoustical) having an essentially constant lateral extent over a specified range. The interrogation beam provides for a well-defined interrogation region which is defined by the substantially constant lateral cross-section over the specified range. The interrogation region may have a relatively sharp illumination boundary, having suppressed or no side-lobes, and within which the interrogation beam's intensity (e.g. integral intensity) is higher than a certain predetermined detection threshold and out of which it is lower than that threshold.
In some cases, the IFF system includes a responder system (e.g. transponder) that is adapted to detect the interrogation beam, determine its intensity and transmit same back to the interrogation system. This allows the interrogation system to assess the quality of the responder's interrogation signal, providing for additional information as to the responder's location within the interrogating beam, and alerting the operator should repeated interrogations with realignment of the interrogation beam be needed. In this manner the IFF of the current invention offers reliability of determining that a responder is located within the prescribed interrogation region or not.
In some cases, an identification friend-or-foe (IFF) system according to the invention may utilize an interrogation wave-beam that maintains a substantially constant lateral extent over a working range of between 200 and 4,000 meters. Such an interrogation wave-beam may be, for example, constructed by a combination of three constituent wave-beams, each with a divergence and intensity selected so as to effect a combined wave-beam that covers an interrogation region/range with good approximation to the desired lateral extent.
In addition to the above, specific configurations of the present invention provide for several additional innovative features that improve the accuracy and reliability of the IFF. Specifically the invention provides for scanning for the responder's location by utilizing several interrogation wave-beams for covering different interrogation regions. For example, in order to refine the interrogation process, the interrogation may be implemented by utilizing two or more interrogation wave-beams sequentially to provide information as to where the responder is situated.
Many of the conventional IFF systems, which utilize optical wave-beams for interrogation, are prone to providing inaccurate and/or unreliable identification and high rates of mis-identifications and/or false alarms. This is due to various factors including the divergence of the interrogation wave-beam, as well as due to varying orientation of the receiving/detector module with respect to the interrogation wave beam (which affects the intensity of the interrogation wave-beam sensed by the receiving module). As a result of the above deficiencies, known IFF systems suffer from relatively deficient reliability.
To this end, the present invention provides various techniques for alleviating these deficiencies. More specifically, except from the use of the interrogation beam having a substantially constant lateral extent, as described above, the present invention also provides improved collection optics which is used, in some embodiments, by the responder system for collecting interrogation wave-beams from various directions.
Yet additionally, according to some embodiments, a novel interrogation protocol or method is provided which is implemented by the IFF system for improving its performance and reducing its energy consumption (specifically at the responder side which is typically battery operated). The interrogation protocol also allows for utilizing low-power and low-cost modules for measuring the intensity/amplitude of the interrogation wave-beam received by the responder. This intensity/amplitude information enables the interrogation system to determine the location of a responder with respect to the interrogation beam with improved accuracy, and indicate the quality of the interrogation response. The interrogation protocol also provides for avoiding interference and jamming of the response signals transmitted by the responder (e.g. by utilizing a frequency hopping technique as well as random delay transmission). The interrogation wave-beam may also be modulated to transmit a code (e.g. identification code) of the interrogator, which is communicated back to the interrogator together with a code/identification of the responder. This protocol allows the interrogator to authenticate the responder and ensure that the response it receives is related to the specific interrogation generated by it (and not to an interrogation of another interrogator). In addition, the code received from the interrogator ensures the responder that the interrogation is a legitimate one (and not a system that has been lost or has fallen into the hands of the enemy for which the codes are not up to date).
Furthermore, state of the art IFF systems are based on direct line-of-sight between the interrogator and the potential target. This limits the application of such systems when a target has been identified briefly but may be hidden from direct sight when an interrogator is activated. This is solved in some variants of the present invention, utilizing an optical wave-beam for interrogation and a radio frequency (RF) for acknowledgement response. The technique of the invention for producing an optical interrogation beam with narrow and well-defined lateral-extent/spot (which may be in the range of 2-3 meters) and with small divergence (e.g. in the range 1 to 6 mrad) allows the operation of the system in near-line-of-sight of the suspect target/responder (e.g. in an urban environment). This is because sufficient energy or power of such narrow and low-divergence interrogation wave-beams can reach the responder via scattering and/or reflection, even if the responder is located behind obstacles such as walls or vegetation obstructing direct line-of-sight between the interrogation system and the responder system. Also, the RF response, which is not directional, can also operate in such a near-line-of-sight condition.
Thus, according to a broad aspect of the present invention there is provided a method for producing a wave-beam having substantially constant lateral extent over a desired range of distances. The method includes generating a plurality of at least partially incoherent constituent wave-beams having different divergences and directing the plurality constituent wave-beams to propagate along substantially parallel propagation axes such that the constituent wave-beams at least partially overlap and superpose to form a combined wave-beam. The divergences and intensities of the constituent wave-beams are selected such that the combined wave-beam has a desired substantially constant lateral extent over a desired range of distances along said propagation axes.
In some embodiments the constituent wave-beams are emitted from one or more output apertures of dimensions significantly smaller than said desired substantially constant lateral extent. In case there are more than one output apertures, the output apertures are arranged such that a distance between propagation axes of any two of said constituent wave-beams is significantly smaller than said constant lateral extent of the desired combined wave-beam.
According to some embodiments of the present invention the plurality of the constituent wave-beams are generated substantially simultaneously, either concurrently or sequentially within a time frame not exceeding a response time of a certain intensity detector. The beams may be continuous wave beams (CW) or pulsed beams, and may be beams of electromagnetic radiation and/or acoustic insonification beams.
Also the cross-sectional shape of the combined wave-beam may take various shapes and may be for example circular and/or elliptic and/or substantially rectangular. According to some embodiments the method further includes adjusting the lateral extent of the desired combined wave-beam by controllably varying at least one of the divergence or intensity of at least one of the constituent wave-beams.
According to another broad aspect of the present invention there is provided a wave-beam generator including: at least one beam source adapted for providing at least one primary wave-beam, and wave directing and focusing module having at least one input port coupled to the at least one beam source and one or more output ports. The wave directing and focusing module includes an arrangement of one or more wave-affecting elements arranged to define a plurality of paths of different focusing powers in between the at least one input port and the one or more output ports and is configured and operable for producing from the at least one primary wave-beam a plurality of at least partially incoherent constituent wave-beams having different divergences. The wave directing and focusing module is also configured and operable for directing the plurality of constituent wave-beams to output from the one or more output ports and propagate along one or more substantially parallel axes of propagation such that the constituent wave-beams at least partially overlap and superpose to form a combined wave-beam. The at least one beam source and wave directing and focusing module are configured and operable for affecting the respective divergences and intensities of said constituent beams such that the combined wave-beam has a desired substantially constant lateral extent over a selected range of distances along the beam propagation axes.
In some embodiments of the present invention the one or more output ports of the wave-beam generator have apertures of dimensions significantly smaller than said desired substantially constant lateral extent, and are arranged such that distances between the propagation axes of the constituent wave-beams are significantly smaller than the desired substantially constant lateral extent of the combined wave-beam.
According to some embodiments of the present invention the wave beam generator is configured for producing one or more groups of constituent wave beams such that each group includes up to four wave-beams having respective linear polarization along desired orientations, each orientation being at least at a 45 degree angle with a preceding orientation and a subsequent orientation. In cases where two more such groups are produced, the different groups may differ from one another in at least one of the following parameters: wavelength, polarization, and path length of their constituent wave-beams.
According to some embodiments of the present invention, the properties of the at least one beam source and/or of one or more of the optical modules are controllable thereby enabling to controllably vary at least one of the following: intensity, divergence, of at least one of the constituent wave-beams. This provides for controlling over the lateral extent of the combined wave-beam.
According to another broad aspect of the present invention there is provided an interrogation system comprising a wave beam generator configured as described above and further described in more details below. In some embodiments the interrogation system also includes a wave-beam generation controller adapted for selectively operating the wave-beam generator module for causing the generation of a desired interrogation wave-beam having a desired substantially constant lateral extent over a selected range of distances along a general direction of propagation of the interrogation wave-beam. This is achieved by operating the wave-beam generator module for substantially simultaneously producing respective constituent wave-beams of a selected combination of wave-beams selected such that superposition of the respective constituent wave-beams forms the desired interrogation wave-beam with the desired lateral extent over the selected range.
In some embodiments of the present invention the interrogation system includes a target detection module including an interrogation wave-beam scanning module. The wave-beam scanning module is adapted for sequentially operating the wave-beam generation controller for sequentially generating two or more interrogation wave-beams associated with at least one of different ranges and different lateral extents thereby enabling determination of a position of a responder system interrogated by one or more of the interrogation beams. In some cases the target detection module is configured and operable for receiving from a responder system an acknowledgment signal encoding intensity data indicative of an intensity of the interrogation wave-beam received by the responder, and processing the intensity data to estimate the location of said responder relative to the interrogating wave-beam.
According to some embodiments of the present invention the interrogation system includes target detection module that is adapted to determine a distance to an interrogated responder utilizing a collective time-of-flight of the interrogation wave-beam and an acknowledgment signal obtained from the interrogated responder in response. The collective time-of-flight may be determined by measuring a time delay between a transmission of the interrogation wave-beam and receipt of the acknowledgment signal and subtracting time delays associated with at least one of the following: internal time delays of the interrogation system, internal time delays of the responder system, and a random time delay by which the acknowledgment signal may have being delayed by the responder.
According to some embodiments the interrogation system includes an interrogation control module adapted for operating said wave-beam generator to encode and/or encrypt data in the interrogating wave-beam. For example, the coding may be in the form of a modulation/pulse sequence of the interrogating wave-beam. In some cases the encoded data may include an initialization sequence including series of initialization segments in said interrogating wave-beam extending over time duration greater than a predetermined standby time duration of a responder system to be interrogated. The responder system may be configured to identify at least one of said initialization segments after recovering from a standby mode of duration not exceeding said standby time duration. In some cases the encoded data includes synchronization data including data indicative of one or more of the following data fields: (i) end-of-initialization data field marking the end of an initialization sequence; (ii) authentication data field indicative of at least one of a type and identity of the interrogating system; and (iii) at least one communication data field indicative of a communication parameter to be used by the target responder system for communication of an acknowledgment response to said interrogation.
According to some embodiments of the present invention the interrogation system further includes a responder system. The responder system includes an interrogation beam receiving module configured and operable for detecting the interrogation wave-beam, and a transmission module, configured and operable for transmitting an acknowledgment communication in response to detection of said interrogation wave-beam. In some embodiments the interrogation beam receiving module includes an optical detector and one or more wave-guiding modules coupled to the optical detector and configured for enabling detection of the interrogation wave-beam by at least two light sensitive faces of the optical detector (e.g. opposite surfaces thereof).
According to some embodiments the interrogation beam receiving module of the responder includes at least three detection modules that are arranged for detecting an interrogation wave-beam propagating towards the responder system from within a horizontal collection angle of at least 180°. For example a detection module may include a detection surface coupled to a collection element having a collection aperture adapted for collecting the interrogation wave-beam propagating thereto from within a certain solid angle and directing the collected interrogation wave-beam to said detection surface. In some cases the collection elements of the at least three detection modules are configured with at least partially overlapping solid collection angles and are arranged such that a total solid angle of collection of the interrogation beam by the interrogation beam receiving module covers at least the solid angle of a hemisphere.
According to another broad aspect of the present invention there is provided an interrogation and response system including an interrogation system and a responder system. The interrogation system includes: a wave-beam generator module configured and operable for producing a plurality of wave-beams having different divergences and substantially parallel axes of propagation, and capable of generating two or more combinations of the wave-beams, such that each combination comprises concurrent production of two or more at least partially incoherent and at least partially overlapping constituent wave-beams of said plurality of wave-beams such a superposition of the respective constituent wave-beams forms an interrogation wave-beam having a desired substantially constant lateral extent over the certain range of distances; and a target detection module comprising a receiver for receiving acknowledgment communication from a responder system detecting said interrogation wave-beam. The responder system includes: an interrogation beam receiving module configured and operable for detecting said interrogation wave-beam, and a transmission module, configured and operable for transmitting an acknowledgment communication in response to detection of said interrogation wave-beam.
According to yet another broad aspect of the present invention there is provided a method for interrogating a responding system. The method includes: generating an interrogation wave-beam by an interrogation system such that the wave-beam is directed towards a responding system being located behind an obstacle along the line-of-sight between said interrogation and responding systems; and detecting a scatter of the interrogation wave-beam from surfaces in the vicinity of the responding system and generating, in response to the detection, an acknowledgement signal capable of bypassing the obstacle. In some embodiments the interrogation wave-beam is characterized by at least one of the following: a substantially constant lateral extent not exceeding 3 meters over a desired interrogation range and relatively small beam divergence not exceeding 6 mrad.
Thus, the present invention provides novel beam generation technique and a novel IFF systems and methods allowing efficient IFF interrogation and response with improved accuracy and reliability. Further aspects and embodiments of the present invention are described in more detail in the detailed description. It will be evident to those skilled in the art that the invention is not limited to the details of the following illustrated embodiments and that the present invention may be embodied in other specific forms without departing from the scope of the attached claims. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive to the scope of the invention, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.